The present invention pertains generally to plastic composite material springs for use as flexible elements in weight bearing structures, and more particularly for use in flexible weight bearing structures such as bedding and seating and furniture.
Springs for use as flexible support elements in support structures such as seating and bedding and furniture have traditionally and conventionally been constructed of spring steel and wire. See, for example, U.S. Pat. Nos. 188,636; 488,378; 1,887,058; 4,535,978; 4,339,834; 5,558,315. Attempts have been made to construct spring support elements out of plastic material. See, for example U.S. Pat. Nos. 4,530,490; 4,736,932; 5,165,125 and 5,265,291. Although fiber reinforced plastic springs are fairly well-developed, the use thereof in flexible support structures such as seating, furniture and bedding presents the formidable engineering challenge of providing suitable means for attachment of the springs to a frame structure and an overlying support surface. Plastic springs have heretofore been simply mechanically attached to a supporting structure such as described in U.S. Pat. No. 4,411,159 on a fiber reinforced plastic leaf spring for a vehicle. Any type of mechanical attachment is complicated by the extreme hardness and stiffness of fiber reinforced plastics.
Ultimately it is nearly always necessary to drill attachment holes in the spring for a mechanical fastener (such as described in U.S. Pat. No. 4,736,932) requiring additional manufacturing and assembly steps. Also, drilling through the fiber-reinforced structure breaks the preferred long strand/roving fibers which are critical to providing optimal spring characteristics. The related application discloses clips for attachment of mattress foundation springs to a frame and an overlying grid. Although fully operative and novel, this approach requires additional parts and increased assembly tasks, and does not entirely overcome the negatives of possible slippage between the spring and the clips, and noise generation by such relative motion.
Conventional bedding systems commonly include a mattress supported by a foundation or xe2x80x9cbox spring.xe2x80x9d Foundations are provided to give support and firmness to the mattress as well as resilience in order to deflect under excessive or shock load. Foundations are typically composed of a rectangular wooden frame, a steel wire grid supported above the wooden frame by an array of steel wire springs such as compression type springs which are secured to the wooden frame. In order to properly support and maintain the firmness level in the mattress, a large number of compression springs are needed in the foundation, resulting in high production cost. This is the main disadvantage of using compression springs in mattress foundations. Also, foundations which use compression springs typically have a low carbon wire grid or matrix attached to the tops of the springs. Both the wires and the welds of the matrix can be bent or broken under abusive conditions. In such steel/metal systems, fasteners are required to secure the springs to the grid and to the frame. This leads to metal-to-metal contact which can easily produce squeaking sounds under dynamic loading.
In an effort to avoid the high cost of using compression springs in foundations, another type of spring used is the torsional steel spring formed from heavy gauge steel spring wire bent into multiple continuous sections which deflect by torsion when compressed. See for example U.S. Pat. Nos. 4,932,535; 5,346,190 and 5,558,315. Because torsional springs are dimensionally larger and stiffer than compression springs, fewer torsional springs are needed in the foundation. However, the manufacture of torsional-type springs from steel wire requires very expensive tooling and bending equipment. Elaborate progressive bending dies are required to produce the complex torsional spring module shapes which may include four or more adjoining sections. The manufacturing process is not economically adaptable to produce different spring configurations without new tooling, tooling reworking and/or machinery set-up changes and process disruption, etc. Therefore, the configuration and resultant spring rate of such springs cannot be easily or inexpensively altered to produce foundations with different support characteristics. Furthermore, the many bends in these types of springs make dimensional quality control and spring rate tolerance control very difficult to achieve. Also, variations in steel material properties and the need for corrosion protection and heat-treating add to the cost and difficulty of producing steel wire spring modules. And furthermore, the awkward geometry of the relatively large torsional springs makes assembly of the springs in the foundation frame relatively difficult.
Another disadvantage of the use of steel wire springs in foundations, and a particular disadvantage of torsional springs, is the phenomenon of xe2x80x9cspring setxe2x80x9d in which a spring does not return completely to an uncompressed height following excessive loading. So long as a spring is deflected within its spring rate tolerance range, it can be repeatedly loaded for a certain number of cycles without noticeable change in operating characteristics. However, if deflected past the maximum deflection range, it will undergo permanent deformation or xe2x80x9csetxe2x80x9d, resulting in a permanent change in operating characteristics such as lack of reflexive support, permanent change in shape, or catastrophic failure in the form of breakage. Spring set in steel wire springs may also occur simply following prolonged normal use, i.e., continuous heavy loading. This phenomenon is also generally referred to as fatigue and can result in catastrophic failure.
In addition, because wood is plentiful, easy to work, and inexpensive, it is an attractive material for use in the frames of mattress foundations. In one embodiment, the frame attachment fittings are configured for lock and key engagement with openings in the top of longitudinal frame members. This requires that the top of the upper longitudinal frame members have holes for engagement with the attachment fittings. However, once a series of holes are placed along the length of a wood frame member, the frame member is no longer capable of providing the support desired in a mattress foundation. Therefore, the present invention also provides another embodiment of the composite spring module adapted for secured engagement to wood frame members. This allows for the production of wood mattress foundations which have all of the advantageous characteristics of the composite material springs but cost less to manufacture than do comparable steel-framed mattress foundations.
In the prior art, wire-type springs have been attached directly to frame members, as for example in U.S. Pat. No. 4,867,424. In the related applications, the composite material springs are designed as low-profile springs. The low-profile springs would be configured with a frame attachment fitting that engages either a wooden frame member or a metal rail such as the patented Sealy Steel Span(trademark) mattress foundation frame rail.
The present invention provides composite material spring modules for use as flexible support elements in support structures such as seating and bedding, and composite material spring modules which can be made in different heights or profiles. In one aspect of the invention, there is provided a spring module having a spring body made of composite material including at least a first plastic material and at least one fiber; and a second plastic material integrally formed about at least a portion of the spring body; attachment fittings made a third plastic material, the attachment fittings including grid attachment fittings configured for attachment to an overlying grid, and at least one frame attachment fitting spaced apart from the spring body by a spacer and configured for indexed engagement with an underlying frame member.
In another aspect of the invention, a single piece composite material spring module has a spring body made of composite material including at least a first plastic material and at least one fiber; and a second plastic material integrally formed about at least a portion of the spring body; attachment fittings made of a third plastic material, the attachment fittings including grid attachment fittings configured for attachment to an overlying grid, the mounting foot configured for direct attachment to a frame member by a fastener, and a spacer for separating the spring body from the mounting foot.
The composite material spring modules include a spring body composed of a plastic enveloping and cured about reinforcing fibers, and a second plastic or polymeric material from which attachment fittings are integrally formed or molded about or bonded to the spring body. The material of the attachment fittings may be the same or different than the plastic material of the spring body. For spring modules for a mattress foundation, the attachment fittings are selectively configured for attachment to members of a foundation frame structure, and to a grid or support structure which overlies the frame structure. The integral formation of plastic attachment fittings about the spring body eliminates the need for physically separate fasteners to secure the springs to the grid. A specially configured mounting foot allows the composite material spring to be mounted directly to a planar surface of a frame member. In one embodiment, a composite material spring module is configured to be attached directly to a frame member which is not otherwise specially configured to engage or receive the spring. The spring module is attached to the frame member by a fastener such as a staple which passes through a mounting portion of the spring module into the frame member.